Multimedia applications are computer programs that provide the capability to generate, transport, and present information in textual, graphic, aural and visual formats. In many multimedia applications, information is generated or stored at devices that are remote from the using devices and human users. In such situations, a communications network must provide the transport mechanisms to users in a timely and efficient manner. Multimedia information, particularly audio and full motion video, has unique properties that impose stringent requirements on the communications network. Unexpected network delays caused by throughput or processing delays can disrupt the presentation of the multimedia data to the end user. An analogy would be trying to carry on a telephone conversation when the network introduced intermittent pauses, delays or slowdowns in the voice stream. Examples of multimedia application that put an emphasis on the network are Client/Server playback of stored multimedia data streams (e.g., library distribution), Client/Client video conferencing, and Client/Client collaborative work.
The property of multimedia information that most significantly affects requirements of the underlying network is the high bandwidth needed to transmit video data, coupled with the requirement of isochronous transmission, that is, the information must be presented to the user in real time and pace. The playback of full-screen, high-quality, stored video and audio at the standard rate of thirty video frames per second; even when compressed, requires approximately 1.2 megabits per second of bandwidth. Four megabits per second or more are required to support two-way video (interactive or conferencing) of high quality. In addition to the high bandwidth requirements, the network must assure that the data is delivered with (a priori) bounded delay. Some communications technologies, particularly time division multiplexing (TDM), are ideally suited to meeting these high bandwidth and bounded delay requirements. Unlike TDM networks, however, packet or cell based networks do not inherently guarantee the delivery of a specified quantity of data in each time interval of a specified duration. Therefore, a method is required in those packet networks to provide equivalent levels of network service for the multimedia applications. This function can be called bandwidth management, or more broadly, quality of service (QoS) management.
Emerging high bandwidth, packet and cell based technologies and architectures (e.g., B-ISDN) anticipate this requirement and thus incorporate techniques to accomplish quality of service management. These techniques typically involve the provision of a sophisticated user network interface through which the user requests a connection for multimedia transport and specifies the quality of service that is required. Within the network itself, sophisticated algorithms are provided to examine the status of resources, compute a route that best satisfies the request, reserve those resources, and notify the user that the connection has been reserved. These algorithms are expensive to implement and are among the most technically demanding functions within the network. They typically require the network to understand the capacity and delay characteristics of each communications link in the network in order to determine whether the quality of service request can be granted. In addition, they require the network to establish, maintain, and update the global network topology information data base in order to determine the optimal route for a connection Most packet based local area networks (LANs), such as token rings (IEEE Standard 802.5), do not offer these sophisticated techniques for quality of service management.
It is extremely desirable to provide apparatus and a method to control multimedia data stream entry into a LAN, based on the quality of service requirements for that particular data stream and the quality of service available in the LAN. The intent of such a technique is to deny network access to those streams whose level of quality of service requirements are not currently available in the LAN network.